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Sunday, 9 October 2011

Skeleton Shrimp

I'm really loving crustaceans! They're so much more interesting and diverse than I had ever imagined. I now realise that I knew almost nothing about them at all!

This little chap is the Skeleton Shrimp, thus named because he looks a tad skeletal. As is so often the case, it's not an actual shrimp at all, but an amphipod.

Less common is that they are an utterly wonderful blend of the sweetly delightful and the scandalously monstrous.
They average out at just 4 centimetres (1.6 inches) in length and they look sort of bent double like an old man (male life veteran?), but they're so thin they also look like a battered, old walking stick that same guy might use.

They are found all over the world, most of them at shallow depths. Their last 3 pairs of legs point backwards and are used for grasping onto algae, plants and other foliage. Some even live on the mouthparts of deep sea crabs!

The rest of the animal points upward, stretching out to catch any algae or detritus that drifts by. But how do they catch these morsels of grub? Why, with big, incredibly vicious claws of course! These fellows aren't vegetarian, but omnivorous. Those grappling hooks can catch hold of small crustaceans to eat, a bit like an underwater Praying Mantis.

The claws are so big and the rest of the body so thin that it puts me in mind of a wiry street boxer. Slim, trim, lean, mean and angry. But probably really nice once you get to know him. It's strange, they look pretty much demonic until you see them living out their lives. Then they become increasingly adorable!

Further up the body are two more, much smaller claws right under the head. All these clawed appendages are used for feeding, which means they're called 'maxillipeds'. But there's also a synonym: gnathopods. I like that a lot more; it reminds me of Gnasher and Gnipper!

Also on the head are 2 pairs of antennae, one really long the other much shorter. Some species use these for filter feeding or scraping algae off various surfaces. I guess when you're stick thin no appendage can go to waste.

Oh, and between the big claws and 3 pairs of grasping legs are a couple gills. It seems that Skeleton Shrimp are so scrawny they can absorb much of the oxygen they need without devoting too many extra body parts to the task.

The gnathopods are also used for getting around. They grab onto a surface before pulling up their rearmost legs and holding on with them so that the gnathopods can let go, stretch out and grab onto something further away. Basically it's just like an inchworm. A skinny, gnarled, shrivelled-up inchworm. Also they can just about swim by repeatedly bending and straightening their body.

Skeleton Shrimp can only mate just after the female has moulted and her exoskeleton is still soft. In some species she may well kill him afterwards with a venomous claw. So maybe she 's not so nice even after you've gotten to know her?

Females hold the eggs in a marsupium on her body. The eggs hatch, the youngsters grow and they all constantly look like they're busting moves on the dance floor!